1. Field of the Invention
The present invention relates to mine roof cable bolts and, more particularly, to coated mine roof cable bolts that are configured to be resin grouted.
2. Brief Description of the Prior Art
A mine roof may be supported by a cable bolt positioned inside a bore hole in a mine roof and resin grouted into place. Examples of mine roof cable bolts are disclosed in U.S. Pat. No. 5,259,703 to Gillespie, U.S. Pat. Nos. 5,375,946 and 5,378,087 both to Locotos, and U.S. Pat. No. 6,074,134 to Stankus et al., herein incorporated by reference.
Cable bolts typically include a single or multi-strand cable segment, a drive head positioned on a first end of the cable segment. A plurality of mixing devices may be positioned along a longitudinal axis of the cable segment, and a stiffening sleeve may be positioned adjacent the first end of the cable segment. These prior art mine roof cable bolts may be tensionable and include one or more mixing devices thereon.
During installation of a cable bolt and mine roof plate system, the first end of a cable segment is generally positioned adjacent a mine roof plate, with the second end inserted into a bore hole created in the earth and rock adjacent a mine roof. Also inserted into the bore hole is a resin catalyst and an adhesive. The cable segment is rotated after insertion, causing the mixing devices to mix the resin catalyst and adhesive. The mixing devices also distribute the adhesive within the rock, in the cracks and crevices between individual strands of a multi-strand cable segment, and in voids between an outer surface of the cable segment and an inner wall of the bore hole. Once cured, the adhesive helps to anchor the cable segment to the earth and rock. Tensionable cable bolts are installed in a similar manner, except that an expansion assembly may also be included to further secure the cable bolt inside the bore hole and tension the bolt between the mine roof and the expansion assembly.
One universal drawback of the cable bolt and mine roof plate systems of the prior art is the trouble and expense associated with incorporating mixing devices, such as nut cages, buttons, or birdcages, into a cable segment. Another drawback is the stiffening sleeve positioned adjacent a first end of the cable segment. In theory, stiffening sleeves help protect the cable segment and prevent the cable bolt from kinking during insertion. However, stiffening sleeves do not prevent torsional deformation of the portion of the bolt not secured in the resin caused when torque is applied to the bolt drive head. When torque is applied during installation of the bolt to mix resin and/or engage a mechanical anchor, a second end of the cable segment decreases rotation as the mechanical anchor and resin restrain movement while the first end is unencumbered. This tends to cause twisting of the cable segment in the portion of the cable bolt between the mine roof and the resin. When installation is complete and torque from the bolt installation machine is removed, the twists in the non-resin grouted portion of the cable untwist which causes the tension applied to the bolt to be reduced. To counteract the twisting of the lower (ungrouted) portion of the cable, a plurality of sleeves or xe2x80x9cbuttonsxe2x80x9d are fixed to the cable lower portion. However, these additional components add to the cost of manufacturing a tensionable cable bolt.
Mixing devices and stiffening sleeves increase manufacturing costs, increase the risk of producing nonconforming goods, and do not prevent torsional deformation. Hence, a need remains for a mine roof cable bolt which resists torsional deformation during installation with subsequent loss of tension, while eliminating or minimizing the need for such extraneous mixing devices and/or stiffening sleeves.
To obviate the deficiencies of the prior art, one embodiment of the present invention generally includes a cable bolt having a coated cable segment. The cable segment generally includes a first end and a second end with a drive head positioned adjacent the first end of the cable segment.
In single cable segments, the coating is positioned adjacent an exterior surface of the cable segment coating all or only a portion of the exterior surface. In multi-strand cable segments, the coating may completely or partially coat an exterior surface of each strand. Positioned adjacent an exterior surface of the coating are particulates forming a textured surface on the exterior of the cable bolt. A tensioning device may also be positioned along a longitudinal axis of the cable segment. The coating serves three primary functions. First, the coating strengthens the cable segment eliminating the need for a stiffening sleeve in some applications. Second, the coating retards torsional deformation of the cable segment bearing the coating when torque is applied to the drive head. Third, the coating further provides an attachment medium for the particulates. The particulates increase the overall surface area of the cable segment providing more bonding area for the resin and providing agitation of the resin catalyst and adhesive during mixing. The particulates, therefore, reduce the need for mixing devices, such as bulbs and birdcages, in some applications.
It is therefore an object of the present invention to provide a cable bolt that resists torsional deformation, does not require a stiffening sleeve, and in some applications, traditional mixing devices.
These and other advantages of the present invention will be clarified in the Detailed Description of the Preferred Embodiments and the attached figures in which like reference numerals represent like elements throughout.